The present invention relates to airbag assemblies, and in particular, to a method of manufacturing inflator assemblies used in airbag assemblies.
It is known in the automotive industry to provide an airbag assembly which inflates upon a motor vehicle collision to protect the passengers within the motor vehicle. The airbag assembly includes a bag member that is normally folded and stored until deployment and an airbag inflator assembly that provides gas under pressure into the bag member to inflate the same during the collision.
Typically, the compressed gas airbag inflator assembly includes a container or bottle for containing compressed gas, a burst disc member for sealing an opening in the container, and an ignitor assembly for generating a force or momentum to burst the burst disc member and thus release the compressed gas from the bottle. The inflator assembly is conventionally assembled in two or more welding procedures. In one procedure, a first side of the burst disc member is welded to a peripheral surface surrounding the opening in the container so that the burst disc is sealed over the opening. In a subsequent procedure, an opposite side of the burst disc member is welded to the housing of the ignitor assembly.
The welding methods heretofore used to weld the burst disc to the container include welding technologies such as tig welds, mig welds, laser welds, friction welds, and electron beam welds. While these technologies have proven to be adequate in accomplishing the desired welded connections, they are unwieldy slow, and/or problematic in that they generate a significant amount of heat that may compromise the integrity of the burst disc member. The burst disc member is typically in the form of a thin metallic disc, having a thickness of only about 0.010"-0.050", and may be compromised by the heat levels utilized during the faster welding processes if some other accommodations are not made. For example, in order to dissipate heat during the welding process, a relatively substantial thermal mass, such as a relatively thick annular metallic ring, may be integrally formed or, otherwise, thermally connected to the ignitor assembly housing or the periphery of the burst disc member before the burst disc member and ignitor assembly housing are welded. Providing this accommodation, of course, adds to the complexity and material cost of manufacturing the entire inflator assembly.
For example, where a separate annular ring is welded between the burst disc and the ignitor assembly housing, an additional welding step is required, and additional material costs are associated with the annular ring stamping. On the other hand, where an annular ring is integrally formed with the burst disc or ignitor assembly housing, the parts must be machined and cannot be stamped in a cost-effective manner. In addition, the additional material for providing the integrally formed thickened portion remains.
It is an object of the present invention to eliminate the disadvantages associated with providing this accommodation. In accordance with this object, the present invention provides an airbag inflator assembly comprising a container, a burst disc member, and an ignitor assembly. The container contains a charge of pressurized gas and has peripheral surface surrounding an opening in the container. The burst disc member has one side welded to the peripheral surface of the container so as to seal the opening and thus confine the charge of pressurized gas within the container. The ignitor assembly includes an ignitor assembly housing and ignition elements constructed and arranged to generate sufficient force to break the seal formed by the burst disc member and release the pressurized gas from the container. The ignition elements are secured to the inflator assembly by the ignitor assembly housing. The ignitor assembly housing is an integrally formed unitary construction welded to a side of the burst disc member opposite the one side.
Another problem associated with conventional techniques of manufacturing the inflator assembly relates to the manner in which the container is pressurized with gas. Conventionally, the burst disc and ignitor assembly are welded in place over a major opening in the container, and the container is pressurized through a smaller diameter opening spaced from the major opening. After the container is pressurized, a small plug or bead is placed over the smaller opening and welded in place, with the gas pressure effectively sealed within the container. This conventional method is time consuming and cumbersome.
It is an object of the present invention to provide a method of manufacturing an airbag inflator assembly which overcomes the difficulties noted above. In accordance with this object, the present invention provides a method of manufacturing an airbag inflator assembly comprising a container constructed and arranged to contain pressurized gas and having an opening defined by a peripheral surface surrounding the opening, a burst disc member constructed and arranged to form a seal with the peripheral surface to seal the opening, and an ignitor assembly constructed and arranged to generate sufficient force to break the seal formed by the burst disc member. The method comprising placing the container, the burst disc member, and a housing for the ignitor assembly in a chamber; pressurizing the chamber to an appropriate pressure based upon a desired pressure to be contained within the container of the airbag inflator assembly; applying force i) to urge a surface portion on one side of the burst disc member and the peripheral surface surrounding the opening in the container into forcible engagement with one another, and ii) to urge a surface portion on an opposite side of the burst disc member and an associated surface portion of the ignitor assembly housing into forcible engagement with one another; applying pulses of electrical discharge i) in the vicinity of the forcible engagement between the surface portion on one side of the burst disc member and the peripheral surface surrounding the opening in the container so that the surface portion on one side of the burst disc member and the peripheral surface surrounding the opening in the container are sealingly welded to one another so that the desired pressure is contained within the container, and 2) in the vicinity of the forcible engagement between the surface portion on the opposite side of the burst disc member and the associated surface portion of the ignitor assembly housing so that the surface portion on the opposite side of the burst disc member and the associated surface portion of the ignitor assembly housing are welded to one another.
These and other objects of the present invention will become more apparent during the course of the following detailed description and appended claims. The invention may be best understood with reference to the accompanying drawings, wherein illustrative embodiments are shown.